> That isn't exactly some subtle side channel involving tiny emissions of radio waves...
No, it seems to be exaclty that. What's non-constant-time is not the execution of the algorithm (as that would probably be exploitable even via USB, worst case), but rather the duty cycle of the externally-observeable RF side channel, if I understand the paper correctly.
Infineon's implementation doesn't seem to be vulnerable to a pure timing attack, as otherwise that RF side channel wouldn't be needed.
They also do implement nonce blinding, but unfortunately with a multiplicative mask significantly smaller than the size of the elliptic curve, so it's brute-forceable.
> What's non-constant-time is not the execution of the algorithm (as that would probably be exploitable even via USB, worst case), but rather the duty cycle of the externally-observeable RF side channel, if I understand the paper correctly.
Are you sure? Section 4.3 (pg 52) starts with "The leaked sensitive information relates to the execution time of Algorithms 1 and 4."
Maybe my terminology is off here, but a "pure time leak" to me would be something like a given operation varying in return time (i.e. execution time/latency being a function of some secret data), whereas this seems more like all operations take constant time, but in that constant time, RF emissions vary in their timing (e.g. on/off, strong/weak etc.) as a function of some secret data.
No, it seems to be exaclty that. What's non-constant-time is not the execution of the algorithm (as that would probably be exploitable even via USB, worst case), but rather the duty cycle of the externally-observeable RF side channel, if I understand the paper correctly.
Infineon's implementation doesn't seem to be vulnerable to a pure timing attack, as otherwise that RF side channel wouldn't be needed.
They also do implement nonce blinding, but unfortunately with a multiplicative mask significantly smaller than the size of the elliptic curve, so it's brute-forceable.